1. Field of the Invention:
The present invention relates to multiple pattern sewing machines and more particularly to a multiple pattern sewing machine wherein the feed amount of cloth and/or the stitch width amplitude are controlled by electronic means.
2. Description of the Prior Art:
Sewing machines have been provided with mechanisms for providing different patterns of stitches in cloth. Normally, each of the different patterns includes a plurality of stitches which may extend various distances laterally and along the feed path and the pattern is repeated after a predetermined number of stitches. Such stitch patterns are obtained by positioning the needle for each stroke thereof at a predetermined position on the cloth (positional coordinates), that is the sewing needle is moved sideways a predetermined distance (stitch width or bight) and the cloth is fed forward or backward a predetermined amount between strokes of the needle. Thus, each stitch pattern comprises a series of positional coordinates for the sewing needle. The required series of positional coordinates for a selected stitch pattern are contained in a memory apparatus in the sewing machine, which memory apparatus is read out upon command and the read out is applied to the feed and bight movement apparatus.
The memory apparatus may be mechanical or electronic. Prior art mechanical memory apparatus normally included cams which were shaped to provide the desired series of positional coordinates. Electronic memories have included a digital type for storage of the series of positional coordinates.
There are many disadvantages to using digital memories for storage of the positional coordinates. The bight and feed movement apparatus are operated by analog signals. The desired analog signals must be converted to digital form for storage, readout digitally and then reconverted to analog form for use. This required a large number of integrated digital circuits which increased the cost of the sewing machine.